TRANSACTIONS OF WAGNER 

 656 



TERTIARY FAUNA OF FLORIDA 



Shell of moderate size and thickness, arcuate below, straight above, with 

 small but prominent prosoccelous beaks ; left valve with twenty-seven square- 

 topped, narrow, entire radial ribs, separated by wider interspaces ; the ribs on 

 the middle of the shell are somewhat narrower than the others; all arc crossed 

 by evenly spaced, moderately prominent elevated lines, festooned in the inter- 

 spaces, and forming small, square ripples on the ribs; both valves similarly 

 sculptured ; cardinal area narrow, with elevated margins behind, wider and 

 short in front of the beaks; the portion in front of the beaks is longitudinally 

 striated, behind the beaks there are three or four concentric, lozenge-shaped 

 groovings ; a single transverse groove usually passes between the beaks ; 

 hinge-line straight ; teeth in two nearly equal series, overlapping a little 

 proximally, the teeth rather crowded and nearly vertical ; base of the valves 

 arcuate, rounded into the anterior end, posterior end a little produced ; in- 

 ternal margins of the valves fluted. Lon. 41, alt. 28, diam. 26 mm. 



This very neat and distinct species appears to be the most common Ark 

 in the upper or Miocene bed at Alum Bluff. 



Scapharca (Anadara) campsa n. s. 

 PLATE 32, FIGURE 21. 



Chesapeake Miocene or upper bed at Alum Bluff, Florida; Dall and 

 Burns. 



Shell of moderate size, solid, and heavy, with a straight and angulatc 

 upper margin, obliquely rounded anterior, produced posterior, and arcuate 

 basal margin ; beaks low, much incurved, mesially impressed, and rather 

 anterior; left valve with about twenty-two narrow ribs separated by wider 

 interspaces, crossed by little elevated, regularly spaced incremental lines; the 

 ribs are not nodulous, the anterior ones are flattish or rarely have a shallow 

 sulcus mesially near the margin; they are subequal, but in specimens in which 

 the mesial depression of the valve is especially strong, the ribs included in it 

 are narrower and closer together than usual ; hinge-line nearly as long as the 

 shell, angular, but not auriculate distally ; the beaks are within the anterior 

 third; cardinal area wider in front, narrow behind, longitudinally striated 

 with a few grooves which circumscribe a " stemmed" arrow-head figure, few 

 of them reaching as far forward as the beaks; teeth in two adjacent series, 

 the anterior shorter with a pronounced thickening of the shell below it, over 

 the vertical face of which the teeth extend rather irregularly or are supple- 

 mented by denticular wrinkles; posterior series longer, numerous, vertical, 



